Suzieseller,
You are mistaken.
You cannot run Snow Leopard, Lion or Mountain Lion on an eMac!
These versions of OS X are for Intel Processor Macs only.
Older Macs, such as an eMac, use Motorola PowerPC processors.
The Intel OS X versions are incompatible.
Petemadeley,
As far as I am aware Apple sales no longer stocks retail versions of OS X 10.5 Leopard.
OS X 10.5 Leopard sold for Apple's original price of $129 U.S.D..
If you can find this online either at the original price, cheaper or a little more expensive than this,this is the OP's only options.
The only options are other online sources.
My advice, forget eBay!
You can still find OS X Leopard 10.5 via Amazon.com.
Since your eMac is only a 700 MHz model, I would not recommend installing or running OS X 10.5 Leopard.
With only a max. RAM of 1 GB of RAM, OS X 10.5 will run as slow as a turtle.
I will make that eMac painfully slow to use!
You need to find black retail discs of OS X 10.4 Tiger.
OS X 10.4 Tiger will run far better on that eMac than OS X 10.5
Also, be advised, you need to determine if your eMac has a drive capable of both reading CDs and DVDs.
Tiger came in both DVD and CD form. If your eMac doesn't have a combo CD/DVD drive and only a CD reading drive, you need to locate the CD set of OS X 10.4 Tiger discs.
Here's an Amazon link to Tiger.
http://www.amazon.com/s/ref=nb_sb_noss_1?url=search-alias%3Daps&field-keywords=O S+X+Tiger
Here's another link for eMac discs both CD/DVD sets s well as a rare set sold with the iWork suite of apps for your eMac.
http://fastmac.com/osx.php
Given how old OS X10.4 Tiger is now, these are not unreasonable pricing for these.
Good Luck to you!